This invention relates to a drum-type facsimile machine capable of transmitting and receiving and in particular to such a machine wherein a plurality of scanning and printing elements are used.
A drum-type facsimile transceiver typically uses a single light-to-electrical transducer provided at a scanning head for use in the transmission mode to scan an image bearing document secured to a rotating drum. The document is scanned when the scanning head is moved axially of the drum by a subscan motor drive as the drum is rotated. The output of the transducer provides data in the form of a continuous serial representation of the light reflected in accordance with the density of the image presented as the document is scanned. The signal from the transducer is digitized or it is used in its analog form. This signal is placed in a suitable form for transmission over a suitable transmission link, such as a telephone line, to another facsimile transceiver having copy paper secured to the drum of the machine. The position and speed of the rotation of the drum at the receiving machine is synchronized with the drum at the transmitting machine. The facsimile transceiver typically has a printer in the form of a single stylus positioned on the scanning head which, when the transceiver is receiving, is positioned in contact with copy paper carried by the drum. As in the case of the transmitting mode, the scanning head is moved axially of the rotating drum at a rate which provides a generally helical scan similar to the scan path provided by movement of the scanning head with rotation of the drum at the transmitting machine. A voltage is applied to the stylus in accordance with the signal received from the transmitting machine causing a reaction at the copy paper surface to produce a representation on the copy paper of the image bearing document scanned at the transmitting machine.
The speed of transmission of such a facsimile machine is limited in part by the transmission characteristics of the transmission link. Various data compression/decompression techniques are known which permit transmission of data over a transmission link at a higher rate. Any increase in the speed of transmission of data sought by an increase in the drum rotation speed of the typical drum/type facsimile machine creates scan and print rate problems as well as vibration and noise problems limiting the increase in copy transmission speed that can be attained by such an approach.